1. Field of the Invention
This invention relates to an image processing method and apparatus. More particularly, the invention relates to an image processing method and apparatus for storing image information that is a mixture of line drawings, such as characters and graphics, and half-tone images such as photographs having color tones.
2. Description of the Related Art
A known method of efficiently storing image information that is a mixture of line drawings (hereinafter referred to as "text"), such as characters and graphics, and half-tone images (hereinafter referred to as "images") such as photographs having color tones involves partitioning the image into small blocks of, say, 8.times.8 pixels each, extracting text, subsequently applying an orthogonal transformation, such as a discrete cosine transformation (hereinafter referred to as "DCT"), coding the coefficients of the transformation and storing the same. Such a method is proposed in the specification of Ser. No. 872,988 (filed on Apr. 24, 1992).
FIG. 26 is a block diagram illustrating an image processing apparatus that relies upon a method of recording image information.
As shown in FIG. 26, image data, which is obtained by combining text with an image, and layout information of this image data are applied to an input terminal 51 from an external device such as a host computer or formatter (not shown).
A data separating circuit 52 separates the image data and layout information from the data entered via the terminal 51. The separated layout information is delivered to a block forming circuit 53, a memory controller (a) 58 and a decoding circuit 62. The separated image data is delivered to the block forming circuit 53.
The block forming circuit 53, to which the image data from the data separating circuit 52 is applied, partitions the image data into small blocks each composed of 8.times.8 pixels.
A text extracting circuit 54 extracts pixels constituting text contained in the 8.times.8 pixel image data (hereinafter referred to as a "block") that has been entered from the block forming circuit 53, stores the results of judging the extracted pixels in a decision memory 57 and an extracted-pixel substitution circuit 55, and stores tone (color) data of the extracted pixels in an extracted-tone memory 59.
In conformity with the results of the judgment from the text extracting circuit 54, the extracted-pixel substitution circuit 55 replaces the pixel data of a block applied thereto through the text extracting circuit 54 by a mean value of pixels excluding the extracted pixels within the block.
The block from the extracted-pixel substituting circuit 55 is applied to a coding circuit 56, which codes the block using a method suited to multivalued image data. Examples of the method are a method proposed by the JPEG, vector quantization, etc.
An image memory 61 stores the code data output by the coding circuit 56.
A printer engine (not shown) is connected to a terminal 65. When the printer engine is started, an engine synchronizing signal enters the memory controller (a) 58 and the decoding circuit 62 via the terminal 65.
The memory controller (a) 58 performs control in such a manner that the data that has been stored in the decision memory 57 and extracted-tone memory 59 is read out in synchronism with an engine synchronizing signal.
On the basis of the engine synchronizing signal and the layout information that has entered from the data separating circuit 52, the decoding circuit 62 outputs a request to a memory controller (b) 60 in such a manner that the image data will be output at a prescribed timing, and then reads the coded data out of the image memory 61. Next, in an image block designated by the layout information, the decoding circuit 62 decodes the coded data from the image memory 61 to obtain a block of decoded data that is output to a rasterizing circuit 63. The decoding circuit 62 further provides the rasterizing circuit 63 with white data outside the image area.
The rasterizing circuit 63 restores the block that has entered from the decoding circuit 62 to the original 8.times.8 pixel image data and delivers the raster image that has been formed to a mixing circuit 64.
In dependence upon the results of judgment read out of the decision memory 57, the mixing circuit 64 mixes the tone data read out of the extracted-tone memory 59 and the raster image input from the rasterizing circuit 63 to reconstitute the image data input from the external host computer or the like, and outputs this image data to the printer engine via a terminal 66.
A disadvantage encountered in the example of the related art described above is that since bitmap data is not handled, it is necessary to mix text with a raster image in the host computer or the like in order to output text data or the like to the printer engine. This leads to two problems, namely (1) data transmission and text mixing require time, and (2) there is no compatibility with the conventional software or formatter, etc.